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Invader No Bigger Than A Grain Of Rice Threatens Avocado Crops

University of Florida

This is a photo of leaves from a redbay tree, one of the native trees vulnerable to the redbay ambrosia beetle that’s threatening Florida’s avocado trees.

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By NEIL JOHNSON | The Tampa Tribune

Published: January 28, 2009

TAMPA - Holy moly, no more guacamole?

An invasive beetle moving through Florida could ravage the state's $30 million-a-year avocado industry as well as thousands of backyard trees.

In the seven years since the redbay ambrosia beetle was discovered in Georgia, it has moved through that state and as far south in Florida as Okeechobee County.

The beetle carries a fungus that causes a condition called laurel wilt, which has proven deadly to a number of tree varieties, including avocado, redbay, camphor and sassafras. Beetles deposit the fungus as they bore into a tree.

The beetles and their young feed on the fungus, which spreads through the tree's vascular tissue, clogging its supply of water and nutrients.

It is a rapid and merciless killer. Once infected, a tree dies in two to four weeks. And once infected, there is no way to save the tree.

In one area, researchers found 90 percent of the host trees were killed within 18 months.

The beetle is native to Southeast Asia and likely hitchhiked to the United States in packing material or pallets. It has been found in nearly 30 counties in southeast Georgia and reached Duval County in Florida in 2005.

Since then, the beetle has expanded to nearly a dozen Florida counties.

It could reach the 7,500 acres of commercial avocado groves in Miami-Dade County in three years, maybe less.

"More likely 18 to 24 months," said Jonathan Crane, a University of Florida professor and tropical fruit crop specialist.

Along the way, backyard avocado trees would also fall to an invader about the size of a grain of rice.

"It's not if," Crane said. "It's when."

Researchers believe the beetle infestation can spread 20 to 30 miles a year.

That's if it doesn't get a boost from people.

In 2005, the beetle jumped from near Gainesville to Indian River County but wasn't found anywhere in between. That means people moved the bug, said Edward Evans, UF professor and agricultural economist.

It's likely someone moved wood from an infected tree, possibly for firewood. In areas where the beetle is common, there are a lot of dead trees. Because the beetles feed on the fungus, they can live and multiply even after the host tree dies.

"People are always looking for firewood," Crane said.

That's why the state Division of Forestry is asking people not to transport firewood.

Even then, scientists see little hope of stopping the beetle's spread. The threat is so new, researchers know little about the insect.

"The insect is not an issue in Asia, so there is not a lot of study," Crane said.

There is a fungicide that may protect redbays and other native trees, but the application and chemicals cost hundreds of dollars per tree, Crane said.

Injecting a poison into a fruit-bearing tree such as an avocado may cause problems with the fruit, he said.

So far, researchers have not found any of Florida's 30 varieties of avocado immune to the beetle's attack.

The state's avocado industry is the nation's second largest. Even if half the trees survive, the total economic loss, including lost wages and money spent for farm supplies and equipment, would be $27 million a year, Evans said.

If the beetle spreads to California, it would find an avocado industry 10 times the size of Florida's.

And Mexico is the hemisphere's largest producer of avocados.

"It's very serious," Crane said. "The problem is so big and so close and so urgent."

Reporter Neil Johnson can be reached at (813) 259-7731 or njohnson@tampatrib.com.

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